Method for filling high aspect ratio via holes in electronic substrates and the resulting holes

ABSTRACT

High aspect ratio (5:1-30:1) and small (5 μm-125 μm) diameter holes in a dielectric substrate are provided, which are filled with a solidified conductive material, as well as a method of filling such holes using pressure and vacuum. In certain embodiments, the holes are lined with conductive material and/or capped with a conductive material. The invention also contemplates a chip carrier formed by such material.

RELATED APPLICATION

This application is a continuation in part of application Ser. No.09/383,325, filed Aug. 26, 1999, for APPARATUS AND METHOD FOR FILLINGHIGH ASPECT RATIO VIA HOLES IN ELECTRONIC SUBSTRATES.

FIELD OF THE INVENTION

The present invention generally relates to a method for filling holes ina substrate and such resulting holes and, more particularly, relates toa method for filling holes in electronic substrates that have highaspect ratios of at least 5:1 in a process for forming vias andinterconnects and the resulting holes and vias.

BACKGROUND OF THE INVENTION

In the electronics packaging industry, there is often a need to fillholes in various substrates for forming vias and interconnects. One suchuse is for a high performance chip carriers having high small diameteraspect ratio holes. The hole filling process is affected by a number ofprocessing and material parameters, for instance, the diameter of thevia hole, the depth of the hole and the type of the substrate material,etc. Typically, via holes are through holes and are used to electricallyconnect a top surface and a bottom surface of a substrate and, thus, thefiller material utilized in forming the vias must be electricallyconductive. A number of techniques have been used to perform the viahole filling process. Depending on the type of the substrate, thetechniques may include electroplating, electroless plating, solder pastescreen printing and conductive paste screen printing.

A fundamental processing problem arises when the depth-to-width ratio,or the aspect ratio grows., The problem gets more complex when the holediameter is made aggressively small, i.e., 125 μm or less. For instance,for holes having depth-to-width aspect ratios of 5:1 or larger, and thehole diameter is less than about 125 μm, it is no longer possible to usea conventional technique such as paste screening to fill the holes. Eventhe more advanced plating techniques cannot be used alone when diametersfurther decrease and aspect ratios further increase.

An attempt to fill via holes that have 17:1 aspect ratio with conductiveepoxies by a screen printing method was found ineffective, even when thescreening process is conducted from both the top and the bottom side ofthe substrate. One other attempt to fill a glass substrate that has viaholes of 17:1 aspect ratio was carried out by utilizing a conductivematerial that has extremely low viscosity, i.e., an eutectic solder thathas a viscosity of only 2 centipoise in its molten state, approachingthat of water. Even at such low viscosity, known techniques for fillingthe high aspect ratio via holes were found ineffective. For instance,the conventional techniques tried include an injection molded soldertechnique with only pressure utilized. The injection molded soldertechnique was not able to fill deep vias holes that have very smalldiameters, i.e., smaller than 25 μm.

A second technique of vacuum injection molding was also tried. A graphicillustration of the vacuum injection molding process is shown in FIGS.1A˜1D. The vacuum injection molding process was disclosed in aco-pending application that was assigned to the common assignee of thepresent invention under Ser. No. 08/518,874. The vacuum injectionmolding method utilizes a pressure differential formed between eitherambient and vacuum or positive pressure and vacuum. The pressure and thevacuum are both supplied on the same surface of a substrate 10, as shownin FIG. 1A. The process is carried out by utilizing a shallow vacuumlink 12 that allows a continual evacuation of air from via holes 20 thathave a large aspect ratio such as 5:1. The vacuum link 12 must besufficiently shallow such that the surface tension of molten solderprevents cross-leaking during the operation. Such a shallow link 12effectively choke a significant part of the full pressure differentialand thus producing only partial filling of via holes 20 that have highaspect ratios.

As shown in FIG. 1A, an injection head 14 which includes spaced apartvacuum slot 16 and injection slot 22 is positioned on top of a moldplate, or substrate 10 in fluid communication with the mold cavities, orvia holes 20 contained therein. Relative axial sliding is effectedbetween the injection head 14 and the mold plate 10 for sequentiallyevacuating gas from the mold cavities 20 using a continuous vacuum andinjecting into the evacuated mold cavities 20 a liquid fed from acontinuous source (not shown). The sliding of the injection head 14 overthe mold plate 10, as shown in FIGS. 1B and 1C, automatically providesself valving for sequentially evacuating and filling the mold cavities20 from the same side, i.e., the top side 18 of the mold plate 10. In apreferred embodiment, the vacuum slot 16 and the injection slot 22 arelinked together at the mold plate 10 so that surface tension of theliquid restrains flow of the liquid (not shown) from the injection slot22 to the vacuum slot 16 while allowing gas flow thereinbetween foreffecting vacuum in the mold cavities 20.

As shown in FIG. 1A, at the start of the process, i.e., before scanningbegins, the mold cavities 20 are empty. As the scanning process begins,as shown in FIG. 1B, some cavities 24 are evacuated. As the scanning ofthe injection head 14 continues, some cavities 26 are filled with theliquid. In the final step of the process, as shown in FIG. 1D, thevacuum supply to the vacuum slot 16 is turned off while the scanning ofthe injection head 14 is completed, i.e., all the cavities 20, 24 and 26are filled with liquid.

The vacuum injection molding method illustrated in FIGS. 1A˜1D applies avacuum and a liquid injection on the same surface of tst be used toallow the continual evacuation of air from mold cavities that have alarger aspect ratio such as 5:1. The drawback of the process is that thevacuum link must be sufficiently shallow such that the surface tensionof molten solder prevents cross-leaking during the operation. Theshallow link chokes off a significant part of the full pressuredifferential and thus only produces partial filling of the moldcavities, or the via holes that have high aspect ratios.

It is an object of the present invention to provide high aspect ratiofilled via holes in an electronic substrate and a method of formingcertain of these filled holes.

SUMMARY OF THE INVENTION

In accordance with the present invention, high aspect ratio filled viaholes in electronic substrates are provided, as well as a method offorming certain of these holes.

In a preferred embodiment, an apparatus for filling a liquid in highaspect ratio holes in a substrate is provided which includes a fillerplate adapted for receiving an injection head therein, the filler platehas a bottom surface adapted for receiving an injection slot provided onthe injection head, a vacuum plate adapted for receiving a vacuum slotin a top surface, the vacuum slot is in fluid communication with avacuum source, and a connection means for connecting the filler plateand the vacuum plate together in a face-to-face, spaced-apartrelationship forming a gap thereinbetween with the bottom surface of thefiller plate positioned parallel and opposite to the top surface of thevacuum plate, the connection means further includes an adjustment meansfor adjusting a relative axial position of the filler plate to thevacuum plate, the gap formed between the filler plate and the vacuumplate is sufficiently large to slidingly engaging a substrate thereinand to form abutting contacts between the substrate and the bottomsurface of the filler plate and between the substrate and the topsurface of the vacuum plate so that holes in the substrate are firstevacuated by the vacuum slot and then filled with a liquid by theinjection slot in the filler plate.

In the apparatus for filling a liquid in high aspect ratio holes in asubstrate, the adjustment means may include a veneer adjustment forfixing a relative axial position of the filler plate to the vacuumplate. The adjustment means may further include a veneer adjustment fortransforming a circumferential displacement into a linear axialdisplacement. The filler plate may be positioned by the adjustment meansto lag behind the vacuum plate such that the injection slot lags behindthe vacuum slot. The filler plate may be positioned by the adjustmentmeans at the same axial position of the vacuum plate such that theinjection slot and the vacuum slot are in fluid communication with ahole in the substrate simultaneously.

In the apparatus for filling a liquid in high aspect ratio holes in asubstrate, the injection slot may have a width sufficiently large tocover substantially all the high aspect ratio holes in the substrate.The injection head may be in fluid communication with a liquid reservoirfor feeding a liquid through the injection slot. The injection slot maybe adapted for feeding a high electrical conductivity liquid soldertherethrough. The connection means may further include an adjustmentmeans of a threaded veneer mechanically attached to the filler plate andat least one engagement pin connecting the threaded veneer to the vacuumplate. The high aspect ratio holes in the substrate are selected fromthe group consisting of via holes, deep through holes and deep trenches.

In the apparatus for filling a liquid in high aspect ratio holes in anelectronic substrate, the high aspect ratio holes may have an aspectratio of at least 5:1, or an aspect ratio of at least 20:1. The highaspect ratio holes may have a diameter not smaller than 5 82 m. Theelectronic substrate may be adapted for making sliding movement betweenthe filler plate and the vacuum plate at a speed of between about 25mm/min and about 250 mm/min. The apparatus may further include a drivemeans slidingly engaging the substrate between the filler plate and thevacuum plate.

The present invention is further directed to a method for filling aliquid into holes that have aspect ratios of larger than 5:1 in asubstrate which can be carried out by the operating steps of providing asubstrate that is equipped with a plurality of through holes that haveaspect ratios of larger than 5:1, each of the plurality of through holeshas a first opening on a first surface of the substrate and a secondopening on an opposite second surface of the substrate, contacting thefirst surface of the substrate with a vacuum plate equipped with avacuum slot such that air is evacuated from the first opening of each ofthe plurality of through holes, and contacting the second surface of thesubstrate with a filler plate equipped with an injection slot such thata liquid can be injected into the second opening of each of theplurality of through holes which was evacuated by the vacuum plate. Themethod also includes forming a conductive cap on the filled hole, orforming a conductive lining in each hole, or both.

The method for filling a liquid into holes that have aspect ratios oflarger than 5:1 in a substrate may further include the step ofcontacting the first surface of the substrate with a vacuum plate andcontacting the second surface of the substrate with a filler platesimultaneously. The method may further include the step of connectingthe vacuum plate to the filler plate by a connection means which furtherincludes an adjustment means of a veneer adjuster. The method mayfurther include the step of adjusting the veneer adjuster such that theinjection slot lags behind the vacuum slot when a substrate is slidinglydisplaced inbetween the filler plate and the vacuum plate. The methodmay further include the step of slidingly engaging a substrate betweenthe filler plate and the vacuum plate, or slidingly moving a substrateinbetween the filler plate and the vacuum plate by a motor means, or thestep of slidingly moving the substrate inbetween the filler plate andthe vacuum plate at a speed between about 25 mm/min and about 250mm/min.

The method for filling a liquid into high aspect ratio holes in asubstrate may further include the step of covering substantially all thethrough holes in the substrate by the injection slots situated in thefiller plate when the substrate is placed between the filler plate andthe vacuum plate. The method may further include the step of connectingthe vacuum plate to the filler plate in such a way that the vacuum plateis situated below the filler plate. The method may further include thestep of providing a pressurized liquid reservoir in fluid communicationwith the injection slot, or the step of feeding a liquid to theinjection slot in the filler plate from a liquid reservoir.

The method may further include the steps of feeding a molten solder in aliquid form to the injection slot in the filler plate, injecting themolten solder into the through holes, and solidifying the molten solderand forming via contacts. The method may further include the step ofconnecting a vacuum evacuation source to the vacuum slot in the vacuumplate such that air is evacuated from the first opening of each of theplurality of through holes.

There is also shown an apparatus for filling an electrically conductivematerial into high aspect ratio holes in an electronic substrate whichincludes a first plate equipped with an injection slot for delivering anelectrically conductive material, a second plate equipped with a vacuumslot for evacuating air, means for fixing the first and second platestogether in a parallely face-to-face, spaced-apart relationship forminga dispensing unit for intimately engaging an electronic substratetherein, the electronic substrate may have holes with aspect ratioslarger than 5:1 therein and the holes are in fluid communication withthe injection slot and the vacuum slot when intimately engaged betweenthe first and second plates, and drive means for causing slidingengagement and relative motion between the dispensing unit and anelectronic substrate positioned therein.

In the apparatus for filling an electrically conductive material intohigh aspect ratio holes, the apparatus may further include anelectrically conductive material reservoir for feeding the material intothe injection slot. The apparatus may further include vacuum evacuationmeans for withdrawing air from the vacuum slot. The fixing means mayfurther include adjustment means for adjusting a relative position ofthe first plate to the second plate, the adjustment means may be aveneer adjuster. The injection slot in the first plate may be adjustedbehind the vacuum slot in the second plate, or the injection slot in thefirst plate may be adjusted to the same axial position of the vacuumslot in the second plate. The electrically conductive material deliveredmay be a molten solder at the lower end of the viscosity range, or aconductive polymer at the higher end of the viscosity range. The drivemeans drives the electronic substrate and cause it to slide between thefirst and second plates. The drive means may be a motor means.

The invention also contemplates a filled hole having an aspect ratio ofgreater than 5:1 and a diameter of less than about 125 μm.

Also contemplated is a filled hole which may be plated with a conductor,and having a conductive cap, or both, and a method of forming such ahole.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionand the appended drawings in which:

FIGS. 1A˜1D are graphs illustrating a vacuum injection molding processwherein a vacuum head and an injection head are mounted on the samesurface of a substrate.

FIG. 2 is an enlarged, cross-sectional view of a substrate havingthrough holes of 17:1 aspect ratio.

FIGS. 3A˜3B are cross-sectional views illustrating the present inventionapparatus in operation.

FIGS. 4A and 4B are cross-sectional views of the present inventionapparatus further equipped with veneer adjustment means.

FIGS. 5A and 5B are a plane view and a cross-sectional view of thepresent invention coating apparatus.

FIGS. 6A and 6B are a cross-sectional view and a plane view of ainterconnect in a liquid crystal display panel formed by the presentinvention method.

FIGS. 7A through 7H show sequentially some of the steps in forming ahigh performance chip carrier having metal filled and metal cappedplated vias.

FIG. 7I shows another embodiment of the chip carrier.

FIG. 7J shows two substrates joined to increase wiring density.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An apparatus and a method for filling high aspect ratio holes inelectronic substrates, which can be advantageously used for forming viacontacts, interconnects or trenches in various electronic structuresincluding but not limited to substrates for display panels, is shown.

Also provided are structures formed by the present method and apparatuswhich have high aspect ratio through holes filled with a conductivematerial such as a conductive polymer or a eutectic solder for providingelectrical communication in an insulating substrate.

The method may be advantageously used to fill deep, high aspect ratiothrough holes such as those having aspect ratios of larger than 5:1, orlarger than 20:1. The present invention novel method can further be usedto fill holes with diameters less than about 125 μm, as small as 10 μm,or as small as 5 μm. In the conventional method, through holes havingdiameters of smaller than 125 μm are difficult to fill with a conductivematerial for forming vias or interconnects.

The method provides for injecting an electrically conductive materialinto via or interconnect holes that have very high aspect ratios. Themethod is a dry processing technique and therefore retains theadvantages of low-cost methods such as paste screening. The method isable to fill via holes that have diameters of 10 μm or larger and aspectratios of 5:1 or larger. The method is made possible by utilizingseveral features such that reliable filling of very deep via orinterconnect holes can be achieved. These features include the use of alarge pressure differential between a filler material supply and the viaholes, positive pressure from the top of the via holes fed from a fillerreservoir and a vacuum from the bottom of the via holes from anevacuation means, an adjustable veneer position arranged between thepressurized supply and vacuum to accommodate various filler viscosities,and a scanning fill method to accommodate a wide range of via hole arraysizes and to ensure fill control.

Referring initially to FIG. 2, wherein an enlarged, cross-sectional viewof a substrate 30 having via holes 32 with high aspect ratios is shown.It should be noted that the via holes 32 are formed in a tapered orhourglass shape in FIG. 2. However, the present invention novel methodis not limited for filling such tapered holes. Holes that have astraight opening may be similarly filled by the present method. As shownin FIG. 2, the narrow center portion 34 of the via hole 32 has adiameter of approximately 30 μm while the spacing between the holes isapproximately 20 μm. The via holes 32 has a length of approximately 500μm and therefore making an aspect ratio of about 17:1. It has been foundthat while a conventional injection molded solder process may beeffective in filling via holes that have aspect ratios up to 5:1 and ahole diameter of larger than 100 μm, the present invention novel methodis capable of filling via holes that have aspect ratios between 5:1 and30:1, and have diameters between about 5 μm and about 125 μm.

Referring now to FIGS. 3A and 3B wherein cross-sectional views of theapparatus 40 are shown. As can be seen in FIGS. 3A and 3B, the methodovercomes the shortcomings of the conventional IMS method by utilizingseveral novel features. First, there are two supplies, i.e., a vacuumsupply and an injection supply that are simultaneous scanned below andabove the stationary via array substrate 42. It should also be notedthat the set-up shown in FIGS. 3A and 3B is more suited for a laboratorytest arrangement. While in a fabrication plant, the filler plate 44 andthe vacuum plate 46 are more likely be held in a stationary positionwhile the via array substrate 42 is scanned through a gap 48 formedinbetween the two plates 44, 46. Since the pressurized filler 50 issupplied to a top opening 52 of the via holes 60 while the vacuum issupplied to the bottom opening 54 of the via holes 60, the full pressuredifferential is produced across the via holes. Since each supply, i.e.,the pressure and the vacuum, may be separately adjusted, a wide range oftotal pressure differentials can be achieved. The wide range of totalpressure differential may be further utilized in conjunction with anadjustable veneer position range shown in FIGS. 4A and 4B.

As shown in FIGS. 3A and 3B, the present method allows for the precisepositioning of both supplies, i.e., the pressure and the vacuum,relative to each other. For example, FIG. 3A shows the vacuum supply 56in front of the pressurized filler supply 58 and therefore, in a leadingor non-overlapping position. FIG. 3B shows the vacuum supply 56 is onlyslightly ahead of the pressurized filler supply 58, and thus in aleading and overlapping position. Each of the relative positions has itsown unique applications depending on the materials utilized and thegeometries of the via holes. A third main position configuration (notshown) is that of the vacuum supply 56 and the pressurized filer supply58 being at the same position, and thus in an equal and overlappingposition. This third position would be suitable for dispensing thehighest viscosity filler materials.

The filler plate/vacuum plate configuration shown in FIG. 3A can besuitably used for lower viscosity materials, such as molten solder. Inthis configuration, there is no overlapping between the scanning vacuumand the pressurized filler supplies. This ensures that the evacuated viaholes 60 (shown in shaded sections) back-fill with molten solder 50without allowing the solder to escape through the vacuum slot 62.Furthermore, the position between both supplies 56, 58 can be preciselypreset such that at a certain scanning speed, i.e., between about 25mm/min and about 250 mm/min, the vacuum does not bleed away before themolten solder fully penetrates the via holes 60. The position settingshown in FIG. 3B, on the other hand, can be suitably used for materialswith higher viscosities. In this configuration, there is some overlapbetween the vacuum and the pressurized filler supplies 56, 58. Thispermits the greatest pressure differential, depending on each supplysetting, to be produced across each via hole 60 for a longer timeperiod. Depending on the scanning speed, this configuration can be usedto fill deep via holes with high-viscosity materials such that longertime is available for penetrating the holes. In the configuration shownin FIG. 3B, it is further possible for some of the via filling material50 to slightly enter the vacuum slot 62 once each via hole is completelyfilled. However, due to the scanning motion of both the filler and thevacuum supplies 56, 58, this can be kept to a minimum required toconfirm complete filling. In effect, the scanning motion essentially“freezes”, or confines the filler material 50 within the vias 60 as theyare sequentially filled and then sealed by the passing slots.

In another configuration shown in FIGS. 4A and 4B, the scanning motionis produced by a mechanical actuator 70 which is connected to the fillersupply plate 44 and the motion is transferred to the vacuum supply plate46 through the engagement pin 66 shown in FIG. 4A. The precisepositioning of the via filler supply 50 in reference to the vacuumsupply 56 is achieved through a veneer positioning adjustment 64 thatlocks in the relative positions of the supply plate 44 and the vacuumplate 46. This precise control is another benefit made possible by thepresent apparatus which can be used to accommodate via filling material50 of various viscosities.

A threaded veneer rod 68 is utilized in the threaded veneer adjuster 64,shown in FIG. 4A, which when turned transforms a circumferential motionof the veneer rod 68 into a linear displacement motion of the fillerplate 44. As a result, a slight change in the vacuum supply plate 46position and its corresponding vacuum slot 62 from the adjustmentposition 1 to the adjustment position 2 shown in FIGS. 4A and 4B,respectively. The engagement pin 66 provides a mechanical link betweenthe filler supply plate 44 and the vacuum supply plate 46. Normally bothplates move in exact unison as they are scanned in reference to thestationary via array substrate 42. Again, it should be emphasized thatin a fabrication plant, it is more convenient and desirable to move thevia array substrate 42 while keeping the filler supply plate 44 and thevacuum supply plate 46 in a stationary position. During veneeradjustment, only one plate is adjusted slightly in position withreference to the other plate through the engagement pin 66. It isobvious that the mechanical actuator 70 can be connected to eitherplate.

FIGS. 5A and 5B show the fixturing 80 that is required to supply amovable vacuum slot 62 and a method for assuring that the via arraysubstrate 42 remains stationary during the scanning operation. A vacuumsupply port 72 may be connected to a vacuum source through a hose. Thevacuum supply port 72 in turn is connected in the fixture to a vacuumsupply channel 74, while the top surface of which is exposed. Themovable vacuum plate 46 covers the vacuum supply channel 74 except forthe area of the vacuum slot 62. This enables the scannable vacuum slot62 as a continuous vacuum source that is readily available. It should benoted that while FIGS. 5A and SB show one specific embodiment of thevacuum plate/filler plate/via array substrate arrangement, it is notintended to limit the scope of the present invention novel apparatus andmethod.

While the present invention novel apparatus and method can be used tofill any type of substrates that are provided with high aspect ratioholes, it is particularly suited for filling deep, high aspect ratio viaholes in substrates such as glass, silicon, plastic laminates, etc.Typical uses of via holes in these substrates include providingelectrically conductive paths from one side of the substrate to theopposite side of the substrate. Such a suitable substrate may be glasswhen used in a display panel application. When the substrates aresilicon, they can be used to fabricate integrated circuits forprocessors and memory devices. Substrates that are made of plasticlaminates are typically used for making high performance (multipleconductive layers separated by insulating layers) carriers that supportsilicon devices. In such applications, the combination of silicon devicemounted on a high performance carrier results in an electronic packagethat can be utilized in many applications, such as PC's,telecommunications, electronic modules for automobiles, etc.

FIGS. 6A and 6B illustrate a cross-sectional view and a plane view ofinterconnects, respectively in a liquid crystal display panel 90 formedby the present invention method. The interconnects formed include thatfor the ground conductors 76, 78 and that for the blue, green and redregions 82, 84 and 86 in the liquid crystal display panel 90,respectively. The interconnects 82, 84 and 86 provide a voltagepotential on the pixel display elements blue, green and red in theliquid crystal layers 88, 92 and 94, respectively. It is seen in FIG. 6Athat the liquid crystal layers 88, 92 and 94 are separated by glassplates 96, 98, 100 and 102, respectively.

The plane view of the liquid crystal display, shown in FIG. 6B,illustrates a plurality of pixels 110 each including the blue, green andred regions that are powered by the interconnects 82, 84 and 86 formedby the present invention novel method. The ground conductors 76, 78 areconnected to the ground plane 106. It should be noted that FIGS. 6A and6B merely illustrate one possible embodiment of a display panel that hasinterconnects formed by the present invention novel method. Theinvention may be equally advantageously applied to other possibleconfigurations of interconnects utilized in other types of displaypanels, i.e, field emission display panels, electro-reflective displaypanels, etc.

Referring now to FIGS. 7A-7H, certain of the steps are shown in forminga high performance chip carrier having metal filled and metal cappedplated through holes or vias. The substrate as shown in FIGS. 7A-7H isshown as a 2S3P core (two signal planes, three power planes) with twoadditional external circuit planes, sometimes referred to as top surfacemetallization and bottom surface metallization. FIG. 7A shows asubstrate 118 just before the plating of the through holes is to takeplace. While several different dielectric materials can be used as thebasis for forming the substrate 118, the preferred and disclosedmaterial is a silica filled polytetrafluoroethylene (PTFE) material,such as that sold by Rogers Corporation under the name “2800-HT”,although other dielectric materials could be used, such as polyimide andepoxy filled fiberglass known as FR4. However, for the present use as ahigh performance chip carrier, silica filled PTFE is preferred. Thesubstrate at the stage of formation as shown in FIG. 7A has been builtsequentially by starting with a ground plane 120 which preferably is a 2mil thick copper-invar-copper (125/75/12.5) material which is etched toform openings, one of which is shown at 122, wherein it is desired tohave the vias, which will be formed later, extend through the groundplane 120 without contact therewith, and one of which is shown at 123,wherein the ground plane 120 will contact the conductive via to beformed later. Silica filled PTFE sheets 124 and 126 are laminated to theopposite sides of the ground plane 120 with layers of copper foil on topof the dielectric layers which are personalized to form signal planes127 and 128. The signal planes 127, 128 are preferably about 12 micronsthick. This assembly constitutes the signal core.

This signal core is then laminated on both sides with layers ofpreferably 1.4 mil thick silica filled PTFE 130 and 132. On top of thelayers 130 and 132 are power planes 134 and 136 which are formedpreferably from layers of copper foil 12 microns thick. The power planesare formed by circuitizing the copper layers 134, 136, which structurethen constitutes the power core. The power core is then subsequentlylaminated with additional layers of silica filled PTFE 138 and 140, eachof which has on its surface thereof a layer of copper foil 142 and 144.The substrate is about 15 mils thick. The surfaces of foil 142 and 144are then thinned, preferably by an etching process known as fluid headetching, as described in U.S. Pat. No. 6,222,136, issued Apr. 24, 2001,entitled “Printed Circuit Boards with Continuous Connective Bumps”,which is hereby incorporated by reference. This results in a thinning ofthe copper foil to a very thin copper film 142 a and 144 a, as shown inFIG. 7B.

At this point in construction, all through holes or openings or vias148, 149 at the required locations are drilled entirely through thesubstrate118. The required vias or through holes 148, which will notallow this ground plane 120 to contact a later filled via and holes 149which will allow the ground plane to control later filled vias, aredrilled through the entire thickness of the substrate 118. These holesare typically 1.5 to 2 mils in diameter.

Following the drilling of the holes, the openings or holes 148, 149, aswell as the surfaces of the copper foil 142 a, 144 a, are seeded with aseed material, such as a PdSn colloidal seed sold by the ShipleyCorporation for Electroless plating, which provides the necessary basisfor electroless plating in the holes 148, 149. (Of course, the seedingon foils 142 a, 144 a is superfluous.) This seed material in the holes148, 149 is shown at 150 in FIG. 7C.

Following the seeding, and as shown in FIG. 7D, copper is electroplated,which results in a copper plating 152 in the opening 148, and copperplating 153 in opening 149, as well as copper plating 154 and 156 on thesurfaces of the copper foil 142 a and 144 a, respectively. The thicknessof the copper plating 152 within the opening 148 is about 0.3 to about0.5 mil thick. Thus, the holes have an aspect ratio of between about 5:1and 30:1, typically about 7:1 and a diameter of between about 5 μm and100 μm, typically about 37 μm.

At this point in the processing of the substrate, the plated holes 148,149 are filled with a liquid conductive material 162, such as a solderor a liquid conductive epoxy, by the apparatus and method as describedpreviously herein. The solder may be any conventional solder. Thefilling process of the holes 148, 149 utilizing the apparatus previouslydescribed provides a vacuum at one end of the openings 148, 149 and apressure fill at the opposite end of the openings 148, 149, all aspreviously described herein. High melting point solder is preferred asthe filling, but not required. For example, eutectic solder can be used.Although solder is the preferred filling material, it is contemplatedthat other conductive liquids that would solidify at room temperaturemay be used, such as Ablestik's Ablebond 8175, DuPont's CB-100, andMulticore Polymet 100. The Ablebond 8175 and CB-100 are silver filledthermoset polymer, and Polymet 100 is a Sn/Cu filled thermoset polymer.The structure at this point is shown in FIG. 7E. It is to be understoodthat the formation of the filled and plated vias as shown herein and aspresently contemplated relies on the filling technique described herein.

Thus, what is formed are drilled vias or plated through holes having anaspect ratio of greater than 5:1, and preferably between 5:1 and 30:1,and having a diameter of less than about 125 microns, preferably betweenabout 5 microns and 125 microns, and more preferably between 5 micronsand 100 microns.

Following the filling of the plated through holes 148, 149, copper iselectroplated on both sides of layers 142 a and 144 a which formscontinuous plating layers 164 and 166 and covers the fill 162 in theplated openings 148, 149. This is shown in FIG. 7F. Following theplating of the layers 164 and 166 these two layers, as well asunderlying layers 142 a and 144 a, are circuitized as shown at 168 and170 which provides circuitization, including caps, over the fillmaterial 162 is shown in FIG. 7G.

Following the circuitization and forming of the caps as shown in FIG.7G, in order to complete the structure for attachment to a chip and asubstrate, soldermask material 172 and 174 is provided on opposite sidesof the opening over the circuitization 168 and 170. This soldermaskmaterial may be a photoimageable material of the type disclosed in U.S.Pat. No. 5,026,624 to Day et al. The soldermask material is exposed anddeveloped to form openings 176 and 178 in the material 172 and 174,respectively. The openings 176 provide for attachment of C4 joints(solder balls) shown in phantom outline at 180 and ball grid arraysolder attachments 182 as shown in phantom in opening 178.

As an alternative to the photoimaged soldermask 172, 174, a soldermaskmaterial, such as a copper/resin laminate sold by Asahi Company underthe designation PCC-5103, can be used. In this case, the copper coatedresin is affixed to the top and bottom surfaces, laser drilled to formblind vias, plated and etched to form the structure, as shown in FIG.71, with a resin coating 190, blind vias 192, having plating 194. Theblind vias serve as connectors for the C4 ball grid array connections.

If desired, several of the substrates formed according to this inventioncan be stacked in superimposed relationship to form a chip carrier withincreased wiring density, as shown in FIG. 7J. In this case, adielectric adhesive sheet 196 is punched or otherwise formed withopenings corresponding to cap 168 in adjacent substrate 118. Solder orconductive paste198 is applied on the caps 168 of one of the substrates118 and the two substrates 118 are laminated together, as shown in FIG.7J.

It is to be understood that the high performance chip carrier ispreferably formed with plated through holes as described. However, thesubstrate can be formed without plating the openings 148, but merelyfilling them with the conductive liquid and letting the liquid solidify.In this case, the plating step is omitted, as well as the seeding step,and the filling is done immediately after the drilling. In this case,the fluid head etching may also be omitted. In any event, the filling isdone using the apparatus and the technique described previously herein.

While the present invention has been described in an illustrativemanner, it should be understood that the terminology used is intended tobe in a nature of words of description rather than of limitation.

Furthermore, while the present invention has been described in terms ofa preferred and two alternate embodiments thereof, it is to beappreciated that those skilled in the art will readily apply theseteachings to other possible variations of the invention.

The embodiment of the invention in which an exclusive property orprivilege is claimed are defined as follows:

What is claimed is:
 1. A dielectric substrate having opposed faces andat least one hole extending completely therethrough from one face to theother, having an aspect ratio of between about 5:1 and 30:1 and diameterat its narrowest point of from about 5 μm to about 125 μm; said holehaving a solidified conductive liquid disposed therein extending fromone end of said hole to the other end of said hole; and wherein said atleast one of said liquid filled hole has a separate, electricallyconductive cap thereon.
 2. The invention as defined in claim 1 whereinsaid hole includes a plating on the surface thereof of an electricallyconductive material surrounding said solidified liquid material.
 3. Theinvention as defined in claim 2 wherein said dielectric substrate has atleast one internal electrically conducting plane in electrical contactwith said electrically conductive material.
 4. The invention as definedin claim 1 wherein said dielectric substrate has at least one internalelectrically conducting plane in electrical contact with said solidifiedconducting material.
 5. The invention as defined in claim 1 wherein saidhole is tapered.
 6. The invention as defined in claim 5 wherein saidhole is generally hourglass shaped.
 7. The invention as defined in claim1 wherein said substrate includes at least two internal power planes. 8.The invention as defined in claim 7 wherein said substrate is a powercore and said cap is a connector pad.
 9. A dielectric substrate havingopposed faces and at least one hole extending completely therethroughfrom one face to the other, having an aspect ratio of between about 5:1and 30:1 and diameter at its narrowest point of from about 5 μm to about125 μm; at least one internal electrically conductive plane in saidsubstrate; said at least one hole having a solidified conductive liquiddisposed therein extending from one end of said hole to the other end ofsaid hole; electrically conductive plating on at least one holesurrounding said solidified material; and each end of each of saidfilled hole having an electrically conductive cap thereon on therespective face of said substrate.
 10. The invention as defined in claim9 wherein said substrate is connected by electrically conductingconnections at one of said end cap to a second structure.
 11. Theinvention as defied in claim 10 wherein said second structure is an I/Cchip.
 12. The invention as defined in claim 10 wherein said secondstructure is a second substrate.
 13. The invention as defined in claim 9further characterized by a soldermask on at least one face of saidsubstrate.